This invention pertains to coating substrates and more particularly to stable, water-borne emulsion compositions containing vinyl chloride polymers.
Vinyl resin lacquers are old in the art and have enjoyed commercial success for coating various substrates with clear vinyl coatings. The coating operation however involves the removal of large quantities of organic solvents in which the vinyl resins are dissolved. For ecological and anti-pollution considerations solvent based coatings are undesirable. This has led to consideration of water-borne resin systems for coating applications. It has not been found feasible to simply substitute a water-borne system for the vinyl resin lacquers for several reasons. While one may make vinyl resin latexes by emulsion polymerization these polymerization techniques require the presence of components in the polymerization recipe which have a deleterious effect on the final coating. This is particularly true in can coatings where such criteria as blush resistance and water resistance, particularly at pasteurization temperatures is required. The presence of surfactants required to maintain stable emulsions increases the susceptibility of resin coatings on substrates to break down in contact with water.
It is also necessary that during the drying stage following the application of the water-borne resin system to a metal substrate that some organic solvent be present to promote proper leveling of the resin to provide a smooth coating.
In the field of can coatings the solution of some problems has led to the creation of new problems. After the hurdles of providing a coating for the interior can which meets physical and chemical criteria have been crossed there still remains the problem of satisfying food and drug regulations.